It is generally well-known that older-model intrusion detector devices could be readily disabled by applying a masking substance, such as, for example, a spray, film, lacquer or opaque sheet over the detector to block the sensor's field of view and prevent it from detecting conditions associated with an unauthorized security breach. For this reason, developers of security devices have been motivated to devise and implement intrusion detectors with anti-mask detection capabilities. Such known anti-mask technologies generally detect when a masking substance has been applied to the detector by either sensing changes in reflectivity or transmittance of light directed at the optical lens or window of the detector.
FIGS. 1A-B and 2A-B illustrate known anti-mask solutions associated with conventional intrusion detectors. In particular, FIGS. 1A and 1B illustrate a detector incorporating mask detection capability by detecting a change in transmittance of light across the lens. The detector illustrated in FIGS. 1A and 1B is shown as having an emitter and detector. In FIG. 1A, the detector is shown in an ordinary condition of use (whereby the detector is operating as designed/intended and capable of detecting/monitoring a designated area). As shown schematically in FIG. 1A, according to existing technologiesan emitter can emit a light across the face of the optical lens and the detector is programmed to detect a baseline transmittance of the light. FIG. 1B illustrates a condition whereby a liquid masking agent such as a spray has been applied across the exterior surface of the lens. According to such a condition, the absorption of the masking agent can reduce the transmittance of the light. The detector is intended to sense this change in transmittance and signal an alarm that the detector has been disabled.
FIGS. 2A and 2B illustrate a conventional detector incorporating mask detection capability through detection of a change in reflectivity of light projected at the lens. The detector of FIGS. 2A and 2B is generally shown as having an internal emitter and detector below (i.e. inside) the lens with the emitter emitting light energy at the lens, the lens (which is typically made of a semi-reflective material) is intended to reflect at least a portion of the light energy back towards the detector. FIG. 2A illustrates a detector in an ordinary condition of use where the detector is programmed to detect a baseline signal from reflection off the interior (A) and exterior (B) surfaces of the lens. FIG. 2B illustrates a condition whereby a liquid masking agent such as a spray has been applied across the exterior surface of the lens. According to such a condition, the reflection of light off the exterior surface of the lens (B) can be reduced, with the detector intended to sense reflection off the masking agent on the exterior surface of the lens (D).
Conventional mask detection technology of the type illustrated in FIGS. 1A-B and 2A-B have a number of limitations. For example, it is generally known that the mask detection capabilities of such devices can be compromised or defeated with the use of a thin, high transmittance and/or low reflectivity masking agent which makes changes to transmittance or reflectivity difficult to detect. Examples of such masking agents can include colorless plastic skins or spray polyurethanes and/or brush-applied clear gloss lacquer. Certifying bodies and/or agencies for intrusion detectors have come to recognize that conventional technologies have difficulty detecting such masking materials and have incorporated detection requirements for such materials as part of the certification evaluation (including, for example certifications for EN-G3 and VDS-Class C standards). In particular, in order for a detector to pass the EN-G3 certification, it must be able to reliably detect the following seven kinds of masking materials:
numberMaterial1.Matt black paper sheet2.2 mm thick aluminum sheet3.3 mm thick clear gloss acrylic sheet4.White polystyrene foam sheet5.Self adhesive clear vinyl sheet6.Colourless plastic skin, spray polyurethane7.Clear gloss lacquer, brush applied
As noted above, detection tests of masking substances 6 and 7 listed above can prove to be especially difficult for conventional detectors to pass on account of known limitations with transmittance change detection or reflectivity change detection. This difficulty is corroborated by tests carried out by Applicant on some of the leading anti-mask intrusion detectors on the market. Specifically, FIGS. 3A-3D show graphical views of a detected signal from an evaluation of a detector in both an ordinary unmasked state (FIGS. 3A and 3C) and in a condition where the detector was masked with a colorless plastic skin/spray polyurethane masking agent (category No. 6 of the EN-G3 certification test) (see FIGS. 3B and 3D). Although this detector registered a pass of the EN-G3 certification test for category 6, the fact that the resulting signals from the masked condition (FIGS. 3B and 3D) are very similar to the signals from the unmasked state (FIGS. 3A and 3C) demonstrates that the masked condition is difficult for the detector to distinguish and/or register.
Some known detectors look to overcome such limitations by incorporating multiple light emitters and multiple receivers to enhance detection of changes in transmittance and reflection (one known detector assembly using as many as four infrared emitters and three infrared photodiode sensors). However, such designs are generally regarded as being more costly from both a materials and manufacturing perspective and more susceptible to failure should one of the emitters/sensors fail or malfunction.
Based on the foregoing, there is a need in the art for a new type of anti-masking device that can detect thin, high transmittance, and low reflectivity masking agents such as colorless plastic skins, spray polyurethanes and brush-applied clear glass lacquers which have proven to be difficult to detect for conventional anti-mask detectors. There is further a need in the art for incorporating such anti-mask capability into an intrusion detector and that such capability be cost-effective and able to reliably meet relevant industry requirements and standards (e.g. EN-G3 and VDS-Class C). There is further a need in the art for a new method for detecting the application of a high transmittance, low reflectivity masking agent to a detector to address limitations of know detector technologies.